Gear drive systems, known in the art, having two gears that rotate in mesh but where one of the gears orbits about the other gear are generally associated with planetary gear arrangements. In planetary gear arrangements, the gears are located in a common plane. Spur or helical gears are generally used in such systems. The teeth of such gear have meshing surfaces which are most commonly portions of involute or cycloidal curves. These curves are commonly truncated by an inner and an outer radius, thus forming the teeth of the gear.
Also known in the art are scroll fluid devices. The generic term "scroll fluid devices" is applied to an arrangement of meshed, involute spiral wraps that are moved along circular translation paths in orbiting fashion relative to each other. This orbiting motion produces one or more fluid transporting or working chambers that move radially between inlet and outlet zones of the device. Such scroll devices may function as pumps, compressors, motors or expanders, depending upon their configuration, the drive system utilized and the nature of energy transferred between the scroll wraps and the fluid moving through the device.
Typically, a pair of scroll wraps will be coupled by an Oldham coupling in order to prevent relative rotational motion between the wraps. Oldham couplings have been used in the prior art between a pair of scrolls to permit one scroll to orbit in a circular path relative to the other scroll. A typical example of a scroll fluid device utilizing an Oldham coupling is illustrated in U.S. Pat. No. 4,178,143 to Thelen et al. In this example, a conventional Oldham coupling maintains a pair of co-rotating scrolls in fixed rotational relationship while permitting their relative orbital movement with respect to each other. In this sense, the Oldham coupling can be viewed as a one-to-one gear drive arrangement that accommodates relative orbital movement between the scroll wraps.
Synchronization of one scroll with respect to the other must be maintained in all scroll machines. If synchronism is lost, gas sealing is ruined and the machine can jam mechanically. In many scroll machines, a steady torque load exists between one scroll and its mate. An Oldham coupling can carry this torque load while preserving synchronization of one scroll with respect to the other. In scroll machines which by their design do not have a steady torque load, there are nonetheless residual stray torques such as from varying friction or gas loads that tends to upset the synchronization of one scroll with respect to the other. An Oldham coupling can be used to carry this stray torque load.
In co-rotating, as well as orbital scroll fluid devices in the prior art, a problem is encountered in using an Oldham coupling. An Oldham coupling consists of three parts: one part on each scroll, and a moving intermediate part that slides linearly with respect to each scroll. The necessary motion of this intermediate or loose part, creates inertia forces that are difficult to balance in either orbiting or spinning scroll machines. If it is balanced, inertia forces will nonetheless have to be carried through its sliding bearing surfaces. If it is not balanced, vibration that results from inertia forces can be reduced by minimizing its mass. But to reduce the mass of the loose part is at the expense of mechanical strength and wear life at the sliding bearing surfaces. The overall performance of a scroll machine increases with increasing rotational speed. At high rotational speeds, it is essential to keep the synchronizer as simple as possible in order minimize the number of available vibrational modes. But an Oldham coupling will always limit the rotational speed of a scroll machine because the mass of the loose part cannot be reduced farther than its strength and wear life will permit.
Other synchronizers known in the art also have speed limitations. Other known synchronizers include the use of a necklace of balls, timing belts and flexgear synchronizers. All of these known synchronizers also include loose parts in addition to the two scrolls. The loose parts of these prior synchronizers move in trajectories that are different from either scroll.
The dynamic behavior of these loose parts at high rotational speed can result in large unsteady inertia forces that cause overall vibration and noise. The loose parts can also have unwanted resonances that magnify the inertia forces to destructive levels. The number of available vibrational modes is large. The occasional and unpredictable instability and rough running of these prior synchronizers can cause a shortened and noisy life. This is especially true in unlubricated scroll machines.
Scrolls can also be synchronized by the action of pins on one scroll plate that orbit within corresponding holes in the other scroll plate. In this type of synchronizer, a third or loose part is not required. But in such synchronizers, the pressure at the contact areas, due to a torque load between the scrolls, is generally so high that only a short life can be achieved.